The present invention relates to an optical information recording/reproducing apparatus for recording and/or reproducing information on optical or opto-magnetic information recording media such as optical disks, and more particularly to an optical information recording/reproducing apparatus with an improved optical head section to reproduce information recorded on the recording media.
Optical information recording/reproducing apparatuses have been utilized in combination with external storage means for computers because information recording media used have larger data storage capacity per unit size thereof. Above all, opto-magnetic information recording media are especially useful owing to its capability of rewriting data. As techniques of recording/reproducing information by the use of such storage means, there are known an inter-mark recording technique (pit position recording technique) and a mark length recording technique (pit edge recording technique). The latter technique is generally thought as more advantageous than the former technique as far as increasing the data capacity. In order to precisely reproduce information from recording media recorded using the latter technique, however, it is required for an optical head section to precisely read edge positions of information bits.
In optical heads for opto-magnetic recording media, data are usually recorded by condensing a light beam of a semiconductor laser as a light source to a small or minute spot, and irradiating the spot light onto a recording medium with the inter-mark recording technique. Also, the information is reproduced by differentially detecting change in the intensity of light resulted from the small spot light being reflected by information bits.
In such a conventional differentially detecting technique, a polarized light beam splitter, the direction of which polarizing axis forms 45 degrees with respect to the direction of polarization of the incident linearly polarized light, is used to divide the reflected light from the recording medium into two beams of signal light. Two signals are respectively detected from both the beams to create a differential signal.
In case the conventional optical head relying on the above-stated differential detection is applied to the mark length recording technique, however, use of single small spot light having a distribution of light intensity like the Gauss distribution so far known in the art would lead to a problem below. Thus, when differentially detecting change in the intensity of reflected light from information bits, a light detector used in the conventional optical head exhibits a reduced edge detecting capability for detection of change in the intensity of entire reflected light, because the distribution of intensity of the irradiated spot light is given by the Gauss distribution spreading to some extent.
The present invention has been made in view of the state of art as mentioned above, and has for its object to provide an optical information recording/reproducing apparatus equipped with an optical head section having a high edge detecting capability when the information recorded by the mark length recording technique is reproduced.
To achieve the above object the present invention provides an optical information recording/reproducing apparatus in which a light beam from a semiconductor laser is led in the form of a small spot by a light irradiating optical system through an objective lens to an information track formed on an opto-magnetic information recording surface, and the light reflected by or transmitted through the information recording surface is led to a light detector by a light receiving optical system through the objective lens, thereby optically reading the information recorded on the information recording surface, wherein the light detector is provided on the optical axis of the light receiving optical system and has an effective light receiving surface almost equal to the airy disk size determined by resolving power of the light receiving optical system, and only that polarized component which is newly produced under the magneto-optic effect, of the polarized component of the reflected or transmitted light, is focused as a light spot onto the light receiving surface through the light receiving optical system, whereby edges of (or between) the information magnetic domains recorded on the information track are detected from a signal output of the light detector.
To achieve the above object, the present invention also provides an optical information recording/reproducing apparatus in which a beam of linearly polarized light from a semiconductor laser is led to an opto-magnetic information recording surface by a light irradiating optical system, and the light reelected by the information recording surface is led to a light detector by a light receiving optical system through the light irradiating optical system so that the information recorded on the information recording surface is reproduced by utilization of the magneto-optic effect, wherein the semiconductor laser has small light emitting areas on both end faces thereof and is provided with a reflection preventive film on at least the end face near the light irradiating optical system; a polarized light selecting optical element allowing the linearly polarized light from the semiconductor laser to pass there-through and a polarizing direction rotator optical element for rotating the plane of polarization of the linearly polarized light by 90 degrees after it reciprocates there-through are both disposed in the light irradiating optical system; and the reflected light from the information recording surface is focused as a light spot again onto the light emitting area of the semiconductor laser by the light irradiating optical system, whereby edges of the magnetic domains as components of the magnetic information recorded on the information recording surface are detected by detecting change in the intensity of light emitted from the semiconductor laser.
To achieve the above object, the present invention further provided an optical information recording/reproducing apparatus in which a beam of linearly polarized light from a semiconductor laser is irradiated in the form of spot light onto an opto-magnetic information recording surface through an objective lens; the reflected or transmitted light of the spot light is separated into a light beam having the polarized component newly produced under the magneto-optic effect at the information recording surface and a light beam having the polarized component perpendicular to the above polarized component; both or either one of the separated two light beams is subjected to adjustment of the light intensity independently; the adjusted two light beams are combined with each other under interference with their directions of polarization aligned with each other; and the composite light beam is focused by a light receiving optical system, whereby edges of the information magnetic domains recorded on an information track of the information recording surface are detected by using output signals from at least two independent light receiving surfaces of a light detector located near the focal point.
To achieve the above object, the present invention still further provides an optical information recording/reproducing apparatus in which a beam of linearly polarized light from a semiconductor laser is irradiated in the form of spot light onto an opto-magnetic information recording surface through an objective lens; a polarizing direction rotator optical element is provided to receive the reflected light beam of the spot light for rotating the direction of polarization of the linearly polarized light by 90 degrees in a partial area of the received light beam; a phase difference adjuster optical element is provided to adjust a phase difference between phase of the light beam in the above area and the light beam out of the above area; the light beam portion rotated in the direction of polarization thereof and the light beam portion not rotated in the direction of polarization thereof are interfered with each other; and distribution of the intensity of the interference light beam is detected by a photoelectric transducing light detector spatially divided into parts, whereby edges of the information magnetic domains recorded on the information recording surface are detected by using a differential signal between output signals from the photoelectric transducing light detector.
To achieve the above object, the present invention still further provides an optical information recording/reproducing apparatus in which a beam of linearly polarized light from a semiconductor laser is irradiated in the form of spot light onto a single information track on the information recording surface of an opto-magnetic information recording medium through an objective lens; the reflected light beam of the spot light is led to a light receiving optical system; the received light beam thus led is divided into first and second regions in the direction of the information track; and the divided light beams are led to a pupil dividing and focusing system for focusing the light beam in the first region onto a first elemental photoelectric transducing light detector and the light beam in the second region onto a second elemental photoelectric transducing light detector, respectively, whereby edges of the information magnetic domains recorded on the information recording surface are detected by using a differential signal between output signals from the elemental photoelectric transducing light detector.